As is well known, the heart muscle effectively acts as a pump which maintains the circulation of blood through the body. More particularly, the left ventricle is that portion of the heart which propels blood in systemic circulation through the body to supply the body tissues with nutrients. In lay terms, this pumping action results from contractions of the heart muscle which are more commonly referred to as the heart beat.
Normally, contractions of the heart muscle (i.e. heart beats) result from an excitation wave of electrical impulses which originate at the atrium, which propagate via the atrioventricular node to the ventricles, and which progress outwardly through conductive tissue in the endocardium. This is normal, and the rhythmic repetition of the heart beat is an indicator of good health. It happens, however, that for a diseased heart there are sometimes variations from the normal rhythm of the heart beat which are manifested as abnormal spontaneous contractions. These abnormalities are clinically referred to as arrhythmia, and they can cause numerous unwanted complications for a patient. Thus, for many reasons, it is desirable to locate the site of arrhythmogenesis or ectopic focus of an arrhythmia with the hope that medical intervention can cure the problem.
As is well known, the ectopic focus of an arrhythmia is usually located in the endocardium. This mislocation of the initiation of contraction from the atrium to what is now the ectopic focus is what causes the arrhythmia. Since heart contractions result from the progression of an excitation wave of electrical impulses, location of the ectopic focus is merely a matter of identifying the point from where the abnormal excitation wave originates. Several catheter electrodes have been proposed for this purpose. The following specifically cited references are representative of these catheters.
U.S. Pat. No. 4,628,937 to Hess et al. for an invention entitled "Mapping Electrode Assembly" is an example of a device which is used for the epicardial or endocardial mapping of the electrical impulses from the heart. According to the teachings of the Hess et al. device, the electrodes are symmetrically arrayed within a mounting cup that conforms to the organ being mapped. Consequently the electrodes of the Hess et al. device are set relative to each other and the efficacy of their displacement is dependent on the ability of the cup to conform to the particular surface.
U.S. Pat. No. 4,699,147 to Chilson et al. for an invention entitled "Intraventricular Multielectrode Cardial Mapping Probe and Method for using Same" discloses a device which positions the electrodes along wire assemblies which can be extended from a catheter to create an elliptical envelope. This envelope is then incrementally rotatable within the heart chamber while electrical potentials are measured and recorded at different points on the endocardium. For this device, all of the electrodes are symmetrically deployed as a unit. Thus, there is no individual control over the placement of any given electrode. Further, there is no assurance that all of the electrodes have, in fact, made contact with the surface of the endocardium.
U.S. Pat. No. 4,522,212 to Gelinas et al. for an invention entitled "Endocardial Electrode" discloses a plurality of spring legs having insulated conductors which are connected to respective sets of spaced electrodes. In operation these spring legs of the Gelinas et al. device are allowed to extend apart to cause the electrodes to engage the wall tissue. Again, as with the other above cited references, there is no individual control over each of the separate electrodes. Consequently, there is no assurance that each electrode is properly placed, or that there is even contact between the electrode and the endocardium.
None of the above examples either individually or collectively disclose the structure or the cooperation of structure which is used to accomplish the objects of the present invention.
In light of the above it is an object of the present invention to provide an endocardial mapping catheter which has a plurality of electrode probes which can each be independently manipulated to achieve non-axisymmetric placement of the electrodes against the endocardium of the left ventricle. Another object of the present invention is to provide an endocardial mapping catheter which establishes a favorable trajectory for each electrode during the placement process that directs the electrode into contact with the endocardium from a direction that is substantially perpendicular to the endocardium. Still another object of the present invention is to provide an endocardial mapping catheter which positions the plurality of electrodes circumferentially against the endocardium in a substantially coplanar arrangement. Yet another object of the present invention is to provide an endocardial mapping catheter which can be positioned, and repositioned, within the left ventricle of a heart to make successive recordings of electrical impulses from the endocardium for use in preparing an isochronal map of these impulses. Another object of the present invention is to provide an endocardial mapping catheter which is easy to use, relatively simple to manufacture, and comparatively cost effective.